Abstract: Interception is a specialized sequence of visual guided actions that occurs when human hands or other body parts initiate an approach to opposing moving target and finally catch them at a certain spatial location. When humans can decide the interception direction of the hand and the time of the startup, what kinds of information do they use to start the interception? It is difficult to estimate time-to-collision (TTC) because the interception zone is not certain. The first aim of the present study was to investigate the role of temporal information and spatial information in hand interceptions of a moving target. In addition, the speed coupling effect has been explained by different and inconsistent theories. The second aim of this study was to examine whether or not this phenomenon existed in free interception and whether or not there was any particular identifiable movement pattern in the interception.
Fifteen undergraduate students participated in the experiment. All of them had normal vision or vision correction to normal. The experiment’s program was run on a Dell computer using Borland C++ Builder. Subjects were asked to hit the moving ball using their index fingers along linear. The tracks of the subject’s hand were recorded by a movement-analysis system based on active infrared markers (Optotrak 3020; Northern Digital). The program also recorded the position of target ball (startup point) when the hand started to move and the distance between the startup point and the interception point when the finger hit the ball. All of the dependent variables were analyzed with repeated measure ANOVA.
The results showed that (1) Different velocities of the target ball influenced the distance and time to collision differently. Time to collision was shorter if the target ball moved more quickly, and it was longer when the target ran more slowly. (2) The startup direction and acceleration of the hand were not affected significantly by the velocity of the target ball. The results did identify a specific movement pattern in the startup of interception.
The conclusions are directed by the study: There is fixed area in interception. It appears that tau and distance may both be used in startup. The speed coupling effect is related to the error of the estimate. The direction and acceleration are stable when subjects start intercepting.

Key words: interception, tau, onset of movement, speed coupling effect